Reinforcing bar binding machine

ABSTRACT

A front end of a loop of a wire fed out to a nose ( 6 ) by a binding wire feeding mechanism ( 1 ) is pinched by a clamp plate ( 28 ) of a binding wire clamping apparatus ( 25 ) and the wire is pulled back by driving to rotate reversely a feeding motor ( 13 ) of the binding wire feeding mechanism ( 1 ). When the wire is brought into close contact with a reinforcing bar (S) and a load of the feeding motor is increased to thereby increase a drive current by a constant amount, a control apparatus stops the feeding motor. Thereafter, the binding wire clamping apparatus ( 25 ) is rotated to twist the binding wire to bind the reinforcing bar. Since the wire is pulled back and a length of the wire is automatically adjusted in accordance with a diameter of the reinforcing bar, a state of finishing to bind the reinforcing bar is made to be uniform and also an amount of consuming the wire is reduced.

TECHNICAL FIELD

The present invention relates to a reinforcing bar binding machine, andparticularly relates to a reinforcing bar binding machine constituted topertinently control a length of a binding wire in accordance with adiameter of a reinforcing bar.

BACKGROUND ART

According to a reinforcing bar binding machine of a background art forbinding a reinforcing bars by feeding a binding wire to form a bindingwire loop around the reinforcing bars and thereafter twisting thebinding wire loop to bind the reinforcing bars, the binding wire iswound around the reinforcing bars by two or more turns to bind andtherefore, there poses a problem that an amount of consuming the bindingwire is large. Further, since an amount of feeding the binding wire isconstant, when a diameter of the reinforcing bar is slender, an amountof twisting the binding wire is increased, a length of a twisted portionis prolonged and therefore, when concrete is cast thereto, the bindingwire is projected from a surface of concrete and a problem may be posedin a finishing.

In order to resolve the above-described drawback, the applicant hasalready proposed a reinforcing bar binding machine constituted such thatone turn of a binding loop is formed by a binding wire feedingmechanism, a front of a binding wire is held by a clamping mechanism andthereafter, a loop diameter of the binding wire is contracted byreversely rotating a motor for feeding the binding wire and thereafter,the binding wire is twisted to bind. However, there are variousboldnesses in the reinforcing bar and a pertinent pull back amount isnot constant. Therefore, when the pull back amount is constituted tocontrol in accordance with a diameter of the reinforcing bar, thebinding can further uniformly be finished. As pull back amountcontrolling means, an amount of reversely rotating a motor for feedingthe binding wire may be adjusted by adjusting means of a dial, a keyswitch or the like, however, such an manual adjusting means is difficultto set pertinently, further, the amount needs to be adjusted each timein accordance with the reinforcing bar diameter, and therefore, this isnot efficient.

DISCLOSURE OF THE INVENTION

Hence, there is posed a technical problem to be resolved in order toachieve constant finishing regardless of a diameter of a reinforcing barby automatically controlling an amount of pulling back a binding wire inaccordance with the diameter of the reinforcing bar and it is an objectof the invention to resolve the above-described problem.

The invention is proposed in order to achieve the above-described objectand provide a reinforcing bar binding machine which is a reinforcing barbinding machine for forming a loop at a surrounding of reinforcing barsby feeding out a binding wire by a binding wire feeding mechanism,clamping a front of the binding wire by a clamping mechanism, pullingback the binding wire by driving to rotate reversely the binding wirefeeding mechanism to wind around the reinforcing bars and twisting thebinding wire by driving to rotate the clamping mechanism to bind thereinforcing bar,

-   -   wherein the reinforcing bar binding machine is provided with a        circuit of detecting a current for driving a feeding motor of        the binding wire feeding mechanism, measures the current for        driving the feeding motor successively at each unit time in a        step of pulling back the binding wire and is provided with a        control portion (controlling means) for stopping the feeding        motor when a newest measured value is increased more than a        lowest value in the measured value by a predetermined amount.

Further, the invention provides the reinforcing bar binding machineprovided with means for detecting an amount of pulling back the bindingwire in addition to the above-described constitution and is providedwith a control portion (controlling means) for stopping the feedingmotor when an amount of pulling back the binding wire reaches areference value in the step of pulling back the binding wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view showing a mechanism portion of areinforcing bar binding machine according to the invention.

FIG. 2 is a plane sectional view showing the mechanism portion of thereinforcing bar binding machine according to the invention.

FIG. 3 is a front view showing the mechanism portion of the reinforcingbar binding machine according to the invention.

FIGS. 4(a) and 4 (b) show a binding wire feeding mechanism of thereinforcing bar binding machine, FIG. 4(a) is a front view and FIG. 4(b)is a side sectional view.

FIGS. 5(a) 5(b) and 5(c) show a step of forming a binding wire path of areinforcing bar binding machine, FIG. 5(a) is a plane sectional view,FIG. 5(b) is a front view and FIG. 5(c) is a side sectional view.

FIGS. 6(a), 6 (b) and 6 (c) show a step of feeding a binding wire, FIG.6(a) is a plane sectional view, FIG. 6(b) is a front view and FIG. 6(c)is a side sectional view.

FIGS. 7(a), 7 (b) and 7 (c) show a step of grabbing the binding wire,FIG. 7(a) is a plane sectional view, FIG. 7(b) is a front view and FIG.7(c) is a side sectional view.

FIGS. 8(a), 8 (b) and 8 (c) show a step of pulling back the binding wireof a binding wire twisting mechanism, FIG. 8(a) is a plane sectionalview, FIG. 8(b) is a front view and FIG. 8(c) is a side sectional view.

FIGS. 9(a), 9 (b) and 9 (c) show a step of refeeding the binding wire,FIG. 9(a) is a plane sectional view, FIG. 9(b) is a front view and FIG.9(c) is a side sectional view.

FIGS. 10(a), 10 (b) and 10 (c) show a step of grabbing the binding wire,FIG. 10(a) is a plane sectional view, FIG. 10(b) is a front view andFIG. 10(c) is a side sectional view.

FIGS. 11(a), 11 (b) and 11 (c) show a step of cutting the binding wire,FIG. 11(a) is a plane sectional view, FIG. 11(b) is a front view andFIG. 11(c) is a side sectional view.

FIGS. 12(a), 12 (b) and 12 (c) show a step of tightening the bindingwire, FIG. 12(a) is a plane sectional view, FIG. 12(b) is a front viewand FIG. 12(c) is a side sectional view.

FIGS. 13(a) and 13 (b) show a twisting step, FIG. 13(a) is a front viewand FIG. 13(b) is a side sectional view.

FIGS. 14(a), 14 (b) and 14 (c) show a state of finishing to twist, FIG.14(a) is a plane sectional view, FIG. 14(b) is a front view and FIG.14(c) is a side sectional view.

FIGS. 15(a), 15 (b) and 15 (c) show a step of opening the binding wire,FIG. 15(a) is a plane sectional view, FIG. 15(b) is a front view andFIG. 15(c) is a side sectional view.

FIG. 16 is a block diagram of an electric circuit of a binding wirefeeding mechanism.

FIG. 17 is a flowchart of controlling the binding wire feedingmechanism.

FIG. 18 is a graph showing a change in a current of driving a feedingmotor.

Further, in notations in the drawings, numeral 1 designates a bindingwire feeding mechanism, numeral 2 designates a binding wire twistingmechanism, numeral 6 designates a nose, numeral 7 designates a baseplate, numerals 8, 9 designate driving gears having V-grooves, numerals10, 11 designate driven gears having V-grooves, numeral 12 designates amiddle gear, numeral 13 designates a feeding motor, numeral 14designates a reduction gear, numeral 15 designates a gear holder,numeral 16 designates a long hole, numeral 17 designates a pin, numeral18 designates a lever, numeral 19 designates a spring receiving seat,numeral 20 designates a compression coil spring, numeral 21 designates atwisting motor, numeral 22 designates a sliding motor, numeral 24designates a ball screw shaft, numeral 25 designates a binding wireclamping apparatus, numeral 26 designates a center clamp plate, numeral27 designates a right front plate, numeral 28 designates a left frontplate, numeral 29 designates a sleeve, numeral 51 designates a controlapparatus, numeral 52 designates a regular and reverse rotation drivingcircuit, numeral 53 designates a revolution number detecting sensor, andnumeral 59 designates a current detecting circuit.

BEST MODE FOR CARRYING OUT THE INVENTION

A detailed description will be given of an embodiment of the inventionin reference to the drawings as follows. FIG. 1 through FIG. 3 show thebinding wire feeding mechanism 1 and the binding wire twisting mechanism2 of the reinforcing bar binding machine, which are included in a casing(not illustrated) having a grip similar to a hand-held tool of a nailingmachine or the like. A wire wound around a wire reel (not illustrated)is supplied to the nose 6 bent in a shape of a circular ark through abinding wire guide hole 5 of a cutter block 4 provided at the noseportion 3 by the binding wire feeding mechanism 1.

FIGS. 4(a) through 4 (b) show the binding wire feeding mechanism 1, thedriving gears 8, 9 having V-grooves are arranged above the base plate 7along a direction of advancing a wire W (binding wire) and two pieces offront and rear driving gears 8, 9 having V-grooves are respectivelybrought in mesh with the driven gears 10, 11 having V-grooves. The twopieces of driving gears 8, 9 having V-grooves are brought in mesh withthe middle gear 12, power is transmitted from the feeding motor (DCmotor) 13 via the reduction gear 14 and the middle gear 12 and the twopieces of driving gears 8, 9 having V-grooves are synchronizinglyrotated.

The two front and rear pieces of the driven gears 10, 11 havingV-grooves are attached to the gear holder 15 in a shape of a bell crank.A middle portion of the gear holder 15 is formed with the long hole 16in a direction orthogonal to a direction of feeding the wire and thegear holder 15 is held pivotably in the front and rear direction and ina left and rear direction by engaging the pin 17 provided at the baseplate 7 with the long hole 16. The base plate 7 is attached with thelever 18 and a front end portion of the lever 18 and a rear end portion(right end portion in the drawing) of the gear holder 15 are coupled bya pin. The compression coil spring 20 is interposed between a rear endportion of the lever 18 and the spring receiving seat 19 provided abovethe base plate 7, the front end potion of the lever 18 and the gearholder 15 are urged in a direction of the driving gears 8, 9 havingV-grooves opposed to each other and the two pieces of driven gears 10,11 having V-grooves are respectively brought into elastic contact withthe driving gears 8, 9 having V-grooves.

In using the reinforcing bar binding machine, the lever 18 is pivoted bypressing the rear end portion of the lever 18 by the finger and the gearholder 15 is moved rearward to thereby bring about a state of separatingtwo pieces of the driven gears 10, 11 having V-grooves from the drivinggears 8, 9 having V-grooves and a front end portion of the wire Wextracted from the wire reel is made to pass between the driving gears8, 9 having V-grooves and the driven gears 10, 11 having V-grooves.Further, when the lever 18 is released from being pressed, the wire W ispinched between the V-grooves of the driving gears 8, 9 having theV-grooves and the driven gears 10, 11 having the V-grooves and thedriving gears 8, 9 having the V-grooves and the driven gears 10, 11having the V-grooves are brought in mesh with each other to prepare foruse.

Although when linearity of the wire is poor, in drawing the wire by thedriving gear 8 having the V-groove and the driven gear 10 having theV-groove from an upstream side (lower side in the drawing), the drivengear 10 having the V-groove may be separated from the driving gear 8having the V-groove by being pressed in a lateral direction, at thisoccasion, the gear holder 15 is pivoted by constituting a fulcrum by thepin 17 and the driven gear 11 having the V-groove on the downstream sidestays to be brought in mesh with the driving gear 9 having the V-grooveto thereby continue feeding the wire W. Further, even when the drivinggears 9 having the V-groove and the driven gear 11 having the V-grooveon the downstream side are deviated from being brought in mesh with eachother by local irregularities of the wire passing the driving gear 8having the V-groove and the driven gears 10 having the V-groove on theupstream side, the driving gear 8 having the V-groove and the drivengear 10 having the V-groove on the upstream side are brought in meshwith each other and the wire is not stopped from being fed.

Next, the binding wire twisting mechanism 2 will be explained. As shownby FIG. 1 and FIG. 2, the binding wire twisting mechanism 2 includes twomotors of the twisting motor 21 and the sliding motor 22, and thetwisting motor 21 drives a final gear 23 via a reduction gear train. Theball screw shaft 24 is fit to a center hole of the final gear 23 by aspline. A male screw is formed at a front end portion of the ball screwshaft 24 and a front end thereof is rotatably coupled with a shaftportion of the center clamp plate 26 constituting a portion of thebinding wire clamping apparatus 25. The binding wire clamping apparatus25 comprises the center clamp plate 26, the clamp plates 27, 28 arrangedon the left and on the right of the center clamp plate 26, the sleeve 29covering three sheets of the clamp plates 26, 27, 28 and a ball holdring 30 fit to a rear end of the sleeve 29 and a ball (not illustrated)fit to a hole of the sleeve 29 is brought in mesh with the male screw ofthe ball screw shaft 24.

When the twisting motor 21 is rotated in a regular direction, the sleeve29 is moved rearward by rotating the ball screw shaft 24. An outerperiphery of the ball hold ring 30 is radially arranged with a rotationstopping fin 31 and at a frontmost position constituting an initialposition, a claw (not illustrated) for stopping rotation provided at thecasing is engaged with the rotation stopping fin 31 of the ball holdring 30 and the binding wire clamping apparatus 25 is brought into anunrotatable state.

A middle portion of the ball screw shaft 24 is attached with a shifterdisk 32 rotatable relative to the ball screw shaft 24. The shifter disk32 is connected to a ball hold ring 34 screwed to a ball screw shaft 33of the sliding motor 22 and the ball screw shaft 24 and the binding wireclamping apparatus 25 of the binding wire twisting mechanism 2 are movedin the front and rear direction in accordance with a direction ofrotating the sliding motor 22.

The left and right clamp plates 27, 28 can be slid to the left and tothe right in parallel with each other along a guide pin 35 provided atthe center clamp plate 26 and guide pins 36, 37 provided at the clampplates 27, 28 are engaged with groove cams 38 formed at inner peripheralfaces of the sleeve 29. The groove cams 38 are reformed by shapes ofapproaching the left and the right clamp plates 27, 28 to each otherwhen the sleeve 29 is moved rearward and finally, the left and rightclamp plates 27, 28 pinch the center clamp plate 26.

Next, operation of the reinforcing bar binding machine will beexplained. FIG. 1 through FIG. 3 show an initial state, when a triggeris pulled from the state, the twisting motor 21 is rotated in theregular direction by a predetermined number of times and as shown byFIGS. 5(a) through 5 (c), the sleeve 29 is moved rearward and the leftand right clamp plates 27, 28 are lightly closed. A binding wire guidegroove 39 for constituting a path for feeding out the wire is formed atthe clamp plate 27 on a right side (upper side in FIG. 5(a)) in viewfrom an operator. The clamp plate 28 on a left side is formed with arecess 40 in a shape of a channel reaching a lower end from an upperportion of an inner side face thereof and in a successive step offeeding the wire, the wire is introduced from a lower side of the clampplate 28 into the recess 40.

Successively, as shown by FIG. 6(a) through FIG. 6 (c), the feedingmotor 13 is started, the wire W reeled out into the nose 6 via the guidegroove 39 of the clamp plate 27 on the right side by rotating the twofront and rear pairs of driving gears 8, 9 having the V-grooves anddriven gears 10, 11 having the V-grooves, is bent in a shape of a loopalong a shape of a guide groove at an inner periphery of the nose 6 andthe front end advances from an opening of a lower face of the clampplate 28 on the left side into the recess 40 and impinges on a ceilingportion of the recess 40 to stop. An amount of feeding the wire W iscontrolled by the control apparatus. Further, notation S designates thereinforcing bar.

The twisting motor 21 is started after stopping the feeding motor 13, asshown by FIG. 7(a) through FIG. 7(c), the sleeve 29 is moved furtherrearward and the clamp plate 28 on the left side is brought into presscontact with the center clamp plate 26 to pinch the front end portion ofthe wire W. Successively as shown by FIG. 8(a) through FIG. 8 (c), thefeeding motor 13 is driven to rotate reversely to pull back the wire Wand a length of the loop is adjusted in accordance with a diameter ofthe reinforcing bar.

FIG. 16 is a block diagram of an electric circuit of the binding wirefeeding mechanism 1 and the control apparatus 51 drives the feedingmotor 13 via the regular and reverse rotation driving circuit 52. Arotation pulse of the feeding motor 13 outputted by the revolutionnumber detecting sensor 53 and a value of a current for driving themotor outputted by the current detecting circuit 59 are inputted to thecontrol apparatus 51 and the control apparatus 51 controls the feedingmotor 13 based on time, the motor revolution number and the motordriving current value.

FIG. 17 shows control steps from starting the binding wire feedingmechanism 1 to a step of pulling back the wire and when the feedingmotor 13 is started by making a trigger switch ON (S1), at the sametime, a timer 51 a of the control apparatus 51 starts measuring a timeof driving the feeding motor 13 to measure an amount of feeding the wire(calculated from the revolution number of the feeding motor 13)(S2).

When a measured time T1 is less than a wire feeding reference time T1_(REF) and a wire feeding amount R1 is less than a reference feedingamount R1 _(REF), in a loop of S3 and S4, the feeding motor 13 iscontinued to drive to rotate regularly, when the wire feeding amount R1reaches the reference feeding amount R1 _(REF), the feeding motor 13 isstopped, counting of time is stopped and measurement of the wire feedingamount is stopped to reset (5S). When a failure in feeding is broughtabout by some cause and the measured time T1 reaches the wire feedingreference time T1 _(REF) before the wire feeding amount R1 reaches thereference feeding amount R1 _(REF), the operation proceeds from S3 toS11 to stop the feeding motor 13.

When the wire is normally fed, after stopping the feeding motor, thefeeding motor is driven to rotate reversely to proceeds to a step ofpulling back the wire. At this occasion, measurement of the driving timeand an amount of pulling back the wire is started, drive current ismeasured at each unit time to store and a newest current value I_(i) anda lowest value I_(LO) of the current value are compared to monitor achange in the current (S6). When a measured time T2 is less than areference time T2 _(REF) of pulling back the wire (incidentally, T2_(REF)<T1 _(REF)) and a pullback amount R2 is less than a referencepullback amount R2 _(REF) (incidentally, R2 _(REF)<R1 _(REF)) and anincrease by a predetermined amount ΔI is not observed in the drivecurrent I_(i), the feeding motor 13 is continued to drive to rotatereversely by a loop of S7→S8→S9.

FIG. 18 shows a change in the current of driving the feeding motor 13, apeak current is made to flow in starting to rotate reversely, the drivecurrent is reduced in accordance with an increase in the revolutionnumber thereafter and at this occasion, the lowest current value I_(LO)is successively updated. Further, when the wire is wound around thereinforcing bar by pulling back the wire, a rotational load is increasedand the change in the drive current I is changed from reduction toincrease. Further, a dotted line indicates a change in the drive currentwhen diameter of the wire is bold and when the wire is bold, aresistance of pulling back the wire is large and therefore, the lowestcurrent value I_(LO) at a point of changing from reduction to increaseis increased. Further, when the newest measured current value I_(i) isincreased from the lowest current value I_(LO) by the predeterminedamount ΔI, the operation proceeds from S9 to S10, the feeding motor 13is stopped to thereby finish the step of pulling back the wire (S10) toproceed to a successive step of twisting the wire.

Further, in the step of feeding out the wire before the step of pullingback the wire, when a failure in a feeding the wire is brought about orthe wire impinges on other hazard and the front end of the wire is notintroduced into between the clamp plate 28 and the center clamp plate 26and the wire cannot be clamped, the pulling back resistance is notincreased and also the drive current I is not increased and when thepulling back amount R2 reaches the reference pulling back amount R2_(REF), the operation proceeds such that S8→S11 and stops the feedingmotor 13. Further, also when the measured time T2 reaches the wirepulling back reference time T2 _(REF), the operation proceeds such thatS7→S11 and stops the feeding motor 13. Here, R2 _(REF)<R1 _(REF) and T2_(REF)<T1 _(REF) and therefore, there is not brought about a situationin which the feeding motor is stopped before the front end of thepulled-back wire passes the driving gears 8, 9 having the V-grooves andthe driven gears 10, 11 having the V-grooves of the binding wire feedingmechanism 1 and the wire must be reset to between the driving gears 8, 9having the V-grooves and the driven gears 10, 11 having the V-grooves.

Further, although according to the embodiment, two sets of the feedingmechanisms combined with the driving gears having the V-grooves and thedriven gears having the V-grooves are provided, one set thereof will do.

Successive to the step of pulling back the wire shown in FIG. 8(a)through FIG. 8(c), as shown by FIG. 9(a) through FIG. 9(c), the wire Wis fed out by a predetermined length by driving to rotate the feedingmotor 13 regularly. The step is for making an amount of projecting of aknot portion uniform by constituting a margin of twisting the wire W bya constant length regardless of a boldness of the reinforcing bar.

Further, as shown by FIG. 10(a) through FIG. 10(c), the sleeve 29 ismoved further rearward, the wire W is solidly pinched by the left andright clamp plates 27, 28 and the center clamp plate 26, as shown byFIG. 11(a) through FIG. 11(c), the sliding motor 22 is driven to rotateregularly and the ball screw shaft 24 and the binding wire clampingapparatus 25 are moved rearward. By moving the binding wire clampingapparatus 25 in parallel with the binding wire guide hole 5 of thecutter block 4, the wire W is sheared at a position of faces of theguide hole 39 of the left clamp plate 27 and the binding wire guide hole5 sliding relative to each other.

Further, as shown by FIG. 12(a) through 12 (c), when the binding wireclamping apparatus 25 is moved further rearward to exert a tension tothe wire W and when the drive current reaches a predetermined upperlimit value by increasing the load of driving the sliding motor 22, thesliding motor 22 is stopped. Further, in the step of tightening thewire, the binding wire clamping apparatus 25 may be moved rearward afterintersecting the wire W by previously rotating the binding wire clampingapparatus 25 by a half rotation.

Next, the twisting motor 21 is driven to rotate regularly, the rotationstopping fin 31 of the ball hold ring 30 moved rearward from the initialposition is detached from the rotation stopping claw of the casing andtherefore, as shown by FIG. 13(a) through 13 (c), the binding wireclamping apparatus 25 is rotated. At the same time, the ball screw shaft24 and the binding wire clamping apparatus 25 are moved forward bydriving to rotate the sliding motor 22 reversely and the binding wireclamping apparatus 25 twists the wire W while approaching thereinforcing bar S.

Further, when the binding wire clamping apparatus 25 is moved forward bya predetermined distance as shown by FIG. 14(a) through 14 (c), or whenthe drive current reaches the predetermined upper limit value byincreasing the load for driving the twisting motor 21 in finishing totwist the wire, the twisting motor 21 and the sliding motor 22 arestopped to drive. Successively, as shown by FIG. 15(a) through FIG.15(c), the twisting motor 21 is rotated reversely, the left and theright clamp plates 27, 28 are opened by moving the sleeve 29 forward,the bound wire W is released and thereafter, the binding wire clampingapparatus 25 is returned to the initial position by controlling thetwisting motor 21 and the sliding motor 22 to thereby finish the bindingoperation of 1 cycle.

Further, the invention is not limited to the above-described embodimentbut can variously be modified within the technical range of theinvention and the invention naturally covers the modifications.

The application is based on Japanese Patent Application (JP-2002-067449)filed on Mar. 12, 2002 and content thereof is incorporated here byreference.

INDUSTRIAL APPLICABILITY

As has been explained above, the reinforcing bar binding machine of theinvention is constituted such that in the step of pulling back thebinding wire, the load for driving the feeding motor is monitored andthe feeding motor is stopped by detecting the increase in the current ofdriving the motor when the binding wire is brought into close contactwith the reinforcing bar and therefore, the length of the binding wireis automatically adjusted in accordance with the diameter of thereinforcing bar to thereby make the state of finishing to bind thebinding wire uniform and also an amount of consuming the binding wire isreduced.

Further, by providing the control means for stopping the feeding motorwhen the amount of pulling back the wire reaches the reference value inthe step of pulling back the wire, when the wire is pulled back in thestate in which the front end of the binding is not clamped by thefailure in feeding the binding wire, the binding wire is prevented frompassing the binding wire feeding mechanism and time and labor of bindingagain the binding wire can be saved.

1. A reinforcing bar binding machine comprising: a binding wire feedingmechanism, including a feeding motor for feeding out a binding wire, forfeeding the binding wire to form a loop around reinforcing bars; aclamping mechanism for clamping a front end of the binding wire; acurrent detecting circuit for measuring a value of a current for drivingthe feeding motor; and a control portion for controlling the feedingmotor; wherein the binding wire feeding mechanism is driven andreversely rotated for pulling back the binding wire and for winding thebinding wire around the reinforcing bars, and the clamping mechanism isdriven and rotated for twisting the binding wire and for binding thereinforcing bar, wherein the current detecting circuit measures thevalue of the current for driving the feeding motor successively at eachunit time in a step of pulling back the binding wire; and wherein thecontrol portion stops the feeding motor when a newest value of the drivecurrent is increased by a predetermined amount from a lowest value ofthe drive current measured in the step of pulling back the binding wire.2. The reinforcing bar binding machine according to claim 1, furthercomprising: a pulling back amount detecting portion for detecting anamount of pulling back the binding wire, wherein the feeding motor isstopped when a pulling back amount reaches a reference value, in thestep of pulling back the binding wire.
 3. The reinforcing bar bindingmachine according to claim 1, further comprising: a revolution numberdetecting sensor for detecting a revolution number of the feeding motor;and a timer for starting to measure a drive time, simultaneously withstarting the feeding motor, wherein an amount of feeding the bindingwire is measured by the revolution number of the feeding motor detectedby the revolution number detecting sensor and the drive time measured bythe timer, in the step of pulling back the binding wire.
 4. Thereinforcing bar binding machine according to claim 3, wherein thefeeding motor is stopped when the time for driving the feeding motorreaches a reference time of feeding the binding wire, in the step ofpulling back the binding wire.
 5. The reinforcing bar binding machineaccording to claim 3, wherein the feeding motor is stopped when theamount of feeding the binding wire reaches a reference feeding amount,in a step of feeding the binding wire.
 6. The reinforcing bar bindingmachine according to claim 1, further comprising: a revolution numberdetecting sensor for detecting a revolution number of the feeding motor;and a timer for starting to measure a drive time, simultaneously withstarting the feeding motor; wherein an amount of pulling back thebinding wire is measured by the revolution number of the feeding motordetected by the revolution number detecting sensor and the drive timemeasured by the timer, in the step of pulling back the binding wire. 7.The reinforcing bar binding machine according to claim 6, wherein thefeeding motor is stopped when the time of driving the feeding motorreaches a reference time of pulling back the binding wire, in the stepof pulling back the binding wire.
 8. The reinforcing bar binding machineaccording to claim 6, wherein the feeding motor is stopped when anamount of pulling back the binding wire reaches a reference pulling backamount, in the step of pulling back the binding wire.
 9. The reinforcingbar binding machine according to claim 1, wherein a predetermined lengthof the binding wire is fed out by driving the feeding motor, after thestep of pulling back the binding wire.
 10. The reinforcing bar bindingmachine according to claim 1, wherein a reference time of pulling backthe binding wire is shorter than a reference time of feeding the bindingwire, and a reference pulling back amount of the binding wire is smallerthan a reference feeding amount of the binding wire.